NAME

SYNOPSIS

DESCRIPTION

This is a graphics format converter from the GIF format to the PNM
(i.e. PBM, PGM, or PPM) format.

If the image contains only black and maximally bright white, the output
is PBM. If the image contains more than those two colors, but only grays,
the output is PGM. If the image contains other colors, the output is PPM.

If you have an animated GIF file, you can extract individual frames from it
with
gifsicle
and then convert those using
giftopnm.

A GIF image contains rectangular pixels. They all have the same
aspect ratio, but may not be square (it's actually quite unusual for
them not to be square, but it could happen). The pixels of a Netpbm
image are always square. Because of the engineering complexity to
do otherwise,
giftopnm
converts a GIF image to a Netpbm image pixel-for-pixel.
This means if the GIF pixels are not square, the Netpbm output image has
the wrong aspect ratio. In this case,
giftopnm
issues an informational message telling you to run
pnmscale
to correct the output.

OPTIONS

--alphaout=alpha-filename

giftopnm
creates a PGM (portable graymap) file containing the alpha channel
values in the input image. If the input image doesn't contain an alpha
channel, the
alpha-filename
file contains all zero (transparent) alpha values. If you don't specify
--alphaout,
giftopnm
does not generate an alpha file, and if the input image has an alpha channel,
giftopnm
simply discards it.

If you specify
-
as the filename,
giftopnm
writes the alpha output to Standard Output and discards the image.

SEE ALSO

AUTHOR

LICENSE

If you use
giftopnm,
you are using a patent on the LZW compression method which is owned by
Unisys, and in all probability you do not have a license from Unisys
to do so. Unisys typically asks $5000 for a license for trivial use
of the patent. Unisys has never enforced the patent against trivial
users, and has made statements that it is much less concerned about
people using the patent for decompression (which is what
giftopnm
does than for compression. The patent expires in 2003.

Rumor has it that IBM also owns a patent covering
giftopnm.

A replacement for the GIF format that does not require any patents to use
is the PNG format.